Definitely attend the interview session the night before.
This is where you get the low down on places from residents AND current applicants. You'll get to see where people applied and what they think and thought about the places (again, residents AND applicants). Also, this may help you figure out what ball game you're in... minors, majors, etc. Strengths, weaknesses, REAL call schedules, etc. will be revealed. You may even find out who's going to interview you and you may find out things about them. Also, you'll meet applicants that you'll meet again and again on the interview trail. It may provide you with a means of cutting travelling costs, etc.
Furthermore, you'll get to see who goes to these things. If residents come, they're more likely sticking up for their program, despite how tired they are. If they don't, it may be a bad sign. Also, chairman and program director's tend to show up to these things. The organizer is usually the residency coordinator, and they will be definitely there. Faculty rarely attend, but they'll ask if you did attend during your interviews. If you didn't attend, everyone (applicants, faculty, secretaries) will ask you why not.
Besides all the **** I just said, you get free food and booze. It's relaxing. And don't show up there in a suit. Shirt and slacks. Tie not necessary, but optional, it seems. No jeans.
For interview suit advice, I'd go with the cleanest, newest looking, blandest suit you have. No cool colors or designs. And this is coming from a dude who is all about fly clothes. If I were interviewing you, I'd like the fly clothes and the earring, but I'm not interviewing you...some old crotchety bastard or bastardette is.
So, in summary, if you're a complete tool and suck socially or if you're inevitably detained by overzealous airport guards, then don't show up. Otherwise, this should be a priority. Therefore, make sure you ask the coordinator about these sorts of events prior to and after interview sessions so that you can plan flights accordingly.
All of the above info is what I have been experiencing on the interview trail this year. And most of it is my biased opinion, of course.